1. Field of the Invention
This document relates to a liquid crystal display, more particularly, to a liquid crystal display which can switch between a wide viewing angle and a narrow viewing angle by comprising white subpixels.
2. Related Art
In the recent information society, display devices have been in the spotlight as visual information transfer media. In recent years, a cathode ray tube or a Braun tube becoming the mainstream is problematic in the heavy weight and bulky size. Various kinds of panel displays which can overcome the limitations of the cathode ray tube have been developed.
Flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panel (PDP) devices and an electroluminescence (EL) displays. Most of these display devices are already available on the market.
Among them, the liquid crystal display device is on a trend of its application scope being broadened due to characteristics such as light weight, thinness, lower power consumption drive and the like. According to this trend, the liquid crystal display devices are used in portable computers, such as notebook PCs, office automation equipment, audio/video equipment, outdoor and indoor advertisement displays, and so on. The liquid crystal display devices control the transmissivity of a light beam in accordance with a video signal applied to a plurality of control switches, which are arranged in a matrix, thereby displaying a desired picture on a screen. Due to the result of research and development and the use of mass production technology, the liquid crystal display device has rapidly been developed to be of large size and high resolution.
Recently, there has been suggested a liquid crystal display device in which pixels formed on a liquid crystal display panel for security and privacy protection comprises a plurality of quad type pixels each having one white subpixel (hereinafter, referred to as “W subpixel”) for viewing angle adjustment and three RGB subpixels, rather than comprising stripe type RGB subpixels. A light blocking member (hereinafter, referred to as “barrier”) is disposed on the W subpixel of the quad type pixels, spaced apart a predetermined gap, and guides light from the W subpixel toward a side viewing angle to reduce visibility from the sides, thereby enabling the implementation of a narrow viewing angle. By such a liquid crystal display device, the switching between a wide viewing angle mode and a narrow viewing angle mode can be arbitrarily controlled by the turn on/off of the W subpixel.
In the wide viewing angle mode, a quad type pixel is driven only by RGB subpixels PR, PG, and PB, with the W subpixel PW being turned off. As the W subpixel PW is turned off, there is generated no leaked light that deteriorates the visibility from a side viewing angle. Since the visibility is maintained well in both of the front and side viewing angle directions, the wide viewing angle mode is implemented.
In the narrow viewing angle mode, a quad type pixel is driven by all of the RGBW subpixels PR, PG, PB, and PW including the W subpixel PW. The W subpixel PW is turned on and the W subpixels PW and the barrier are spaced apart a predetermined gap from each other. Thus, from a side viewing angle, as shown in the drawing, the visibility is reduced much due to the affect of a leaked light from the W subpixel PW. On the contrary, from the front viewing angle, a leaked light from the W subpixel PW is blocked by the barrier. In this manner, while the visibility is maintained well in a front viewing angle direction, the visibility is lowered much in a side viewing angle direction, thereby implementing the narrow viewing angle mode.
By the way, as stated above, the liquid crystal display device having such a quad type pixel structure has the barrier spaced apart a predetermined gap from W subpixels PW. Hence, the degree of light shielding of the barrier on the RGB subpixels PR, PG, and PB in the side viewing angle directions is varied according to a viewing angle. For example, as shown in FIG. 3, there is a big difference in the degree of light shielding by the barrier among an image of the B subpixels PB viewed from □, an image of the G subpixels PG viewed from □. The difference in the degree of light shielding of the barrier on the RGB subpixels PR, PG, and PB leads to a difference in the size of RGP aperture regions exposed according to a side viewing angle, and this occurs in both of the wide viewing angle mode and the narrow viewing angle mode.
When the size of RGP aperture regions exposed in a side viewing angle direction is varied according to a viewing angle, if all of the subpixels of the quad type pixel as shown in FIG. 4 are fixedly disposed at specific positions, the observer senses the image of the B subpixels PB relatively much less than the images of the R and G subpixels PR and PG from a side viewing angle. This causes a greenish or yellowish color shift at a side viewing angle, and hence acts as a primary factor to destroy white balance and deteriorate display quality at a side viewing angle.